Flexible and transparent sensors have a wide variety of applications. For example, such sensors may be used on electronic devices, such as display and input devices, and wearable or implantable electronic devices. These sensors also have applications in medical or healthcare industries.
Commonly used flexible and transparent conductive materials include thin metal strips, wires, or nanotubes, or very thin metal coatings. Silver nanowire has been found suitable for use in capacitive sensor touch panels or touch sensor films. Indium tin oxide (ITO) has also been used as conductive materials in inflexible and transparent sensors. Highly transparent ITO can have sheet resistance above 100Ω/□. The sheet resistance of an ITO material can be as low as 30 to 40Ω/□ when its transparency is in the range of 83 to 88%. Typically, these conductive materials conduct electrical currents or transmit signals by way of electron movement in the material. However, these materials have some limitations and drawbacks and efforts have been made to find replacement or alternative conductive materials.
Sun et al. discloses an ionic skin used as a pressure sensor, which includes ionic conductors formed from acrylamide (AAm) based hydrogels. The sensor can detect pressure of touch by a finger on the ionic skin. See Sun et al., “Ionic skin,” Advanced Materials, first published online Oct. 29, 2014, DOI:10.1002/adam.201403441 (referred to as “Sun” hereinafter). In an ionic conductor, electrical signals are transmitted due to ion movement within the conductor. Sun notes that its ionic skin is highly strethchable, transparent, and biocompatible, and can be used to monitor larger deformation such as that generated by bending of a finger. It is reported to be able to detect stimuli with a wide dynamic range (strains from 1% to 500%), and to measure pressure as low as 1 kPa. A sheet of distributed sensors covering a large area can report the location and pressure of touch. High transparency allows transmission of electrical signal without impeding optical signals.